Load compensated car dumper clamp

ABSTRACT

There is provided an improved hydraulic clamping apparatus which is characterized by hydraulically actuated extensible arm means coacting between first and second jaw members for moving them toward and away from each other. One of the jaw members is equipped with an abutment and means for anchoring the extensible arm thereto. These means comprise a floating and loadcompensating mounting plate secured to the arm and constructed for seating engagement against the abutment in opposition to a load which tends to separate the jaw members. When the load on the arm exceeds a predetermined amount, the floating mounting plate is adapted for movement away from the abutment. Resilient means are provided for biasing the mounting plate against the abutment with a predetermined prestressed force which sets or determines the load at which the mounting plate will float away from the abutment. In this way, the loads are decreased and shock loads on the clamping equipment are readily endured and damage to the clamping mechanism and cars is minimized. Clamps embodying the features of the present invention are particularly useful for holding gondola-type railroad cars in a rotary dumper.

[451 Sept. 25, 1973 United States Patent [1 1 Haditsch paratus which is characterized by hydraulically actu- LOAD COMPENSATED CAR DUMPER CLAMP ated extensible arm means coacting between first and second jaw members for moving them toward and away from each other. One of the j aw members is equipped [75] Inventor: Karl Haditsch, Seven Hills, Ohio [73] Assignee: McDowell-Wellman Engineering with an abutment and means for anchoring the extensians comprise a floating and -compensating mounting plate secured to the arm and constructed for seating en ab ble arm thereto. These me load Company, Cleveland, Ohio Nov. 17, 1971 [22] Filed:

gagement against the [21] utment in opposition to a load which tends to se rate the jaw members. When the load on the arm Appl. No.: 199,588

[52] US. Cl.....

ceeds a predetermined amount, the floating mounting [51] Int Cl 4, plate is adapted for movement away from the abut- 56 g269/25 ment. Resilient means are provided for biasing the mounting plate against the abutment with a [58] Field of Search predetermined prestressed force which sets or determines the load at which the mounting plate will float away from the abutment. In this way, the loads are decreased and S T N m MA .IP a M e me. e m N N U N H /5 shock loads on the clamping equipment are readily endured and damage to the clamping mechanism and cars 214/55 is minimized. Clamps embodying the features of the present invention are particularly useful for holdin gondola-type railroad cars in a rotary dumper.

X 5 H 4 l 2 1,821 ,2l7 9/1931 Heaton et a1. 1,465,006 8/1923 Simpson et al. 3,232,459 2/1966 Sabin Primary ExaminerRobert G. Sheridan Attorney-Harold F. McNenny et a1.

11 Claims, 5 Drawing Figures [57] ABSTRACT There is provided an improved hydraulic clamping ap- PArEminszrzsma SHEET 2 OF 3 KARL HAD/TSCH PAliNTfnstrzslsn SHEET 3 0F 3 INVENTOR. mm. HADITSCH ATT LOAD COMPENSATED CAR BUMPER CLAMP BACKGROUND OF THE INVENTION AND PRIOR ART The present invention is concerned with clamps in general, and more particularly to clamps which are especially adapted for holding railroad cars of the gondola type in a rotary railroad car dumper during inversion to empty the contents of the car. Numerous types of clamps, ranging from cable-operated clamps to hydraulic extensible arm-type clamps, have been used for the purpose of grasping and holding railroad cars during inversion thereof to remove the contents. The hydraulic extensible arm-type clamps are preferred over the cable-operated type clamps because the clamping action is more positive and is sustained during the entire cycle. Reference may be had to the U.S. Pat. to Crist, No. 2,381,723, the U.S. Pat. to Kincaid, No. 2,659,500, the U.S. Pat. to Ludwig, No. 3,337,067, and the U.S. Pat. to Sabin, No. 3,232,459 as exemplary of these types of rotary car dumper clamps.

When used in a rotary railroad car dumper, the new clamps of the present invention are characterized by an ability to compensate for changes in the clamp force between the top of the car and the clamp as the car is rotated to an inverted position. This ability minimizes damage to the car and to the car clamps and thus reduces maintenance of these components. Since the forces are smaller, the size and cost of the clamp mechanism is also reduced. The improved clamping mechanisms of the present invention permit expansion of the railroad car springs during the full rotation cycle. With conventional clamps, the railroad car springs are able to expand only for the initial 75 of rotation. Even under optimum conditions, conventional railroad car clamps will relieve only 35 percent of the railroad car spring force. The improved devices of the present invention are capable of relieving up to 100 percent of the railroad car spring forces. These devices will also permit-higher speeds of clamping since they are capable of absorbing the oil flow impact when the clamp suddenly engages the top of the railroad car. These devices also act as shock absorbers when the clamp is lifted and suddenly stopped in a position intermediate of the full stroke of the hydraulic extensible arm.

Among the advantages of the clamping mechanisms of the present invention'when used as clamps for gondola-type railroad cars is the ability to relieve the railroad car springs. This is a most desired characteristic of these devices. Railroad car spring relieving may be explained as follows: The weight of a railroad car and the weight of the material in the car is supported on springs which are located in the car trucks. A loaded railroad car is, therefore, lower in height than an empty car. The difierence in height is due to spring compression. When the car clamps of a rotary railroad car dumper engage the top of the car and the clamps are latched or locked, the railroad car springs in conventional devices are still almost fully compressed with a force which equals the sum of the car weight and the material weight. Normally, in conventional devices the clamps are or become locked at approximately 70 of dumper rotation. As the dumper rotates beyond the 70 position to 155 or 180 of rotation, the material in the car is discharged. However, the locked car clamp engaging the top of the car prevents railroad car spring travel and the trapped-in spring force is now pushing on the car clamp in addition to the car weight and the weight of any material which does not flow out, for example, because of being frozen. With the dumper in the fully rotated position and the car in almost. upsidedown position, the forces on the clamps on conventional dumpers equals the trapped-in car spring force which almost equals the full weight of the material in the car plus the weight of the car. Additional clamp forces will result when material is frozen in the car and remains in the car while it is inverted All of these high forces are frequently damaging to the top of the cars and to the clamping mechanism. An important object of the present invention, therefore, is to reduce this locked-in car spring force and thus prevent damage to the car and to the clamp.

Another important factor of the present mechanism is that it is capable of reducing oil fluid hammer. When the car clamps engage the top of the car, they are traveling with a speed which is proportional to the oil flow from the hydraulic pump to the piston. This oil flow in a conventional hydraulic clamp is then suddenly stopped when the clamp hits the top marginal edge of the car. The shock pressure of the suddenly stopped oil flow is superimposed on the pump pressure which results in high peak pressure for which the cylinder and piping must be designed. The new car spring-relieving mechanism will absorb this fluid flow shock. Pressures in the hydraulic cylinderl'which-are greater than the preset pump pressure will cause a compression of the resilient means and cushion the impact. The cushioned impact will permit higher clamp speeds and reduce impact pressure and fluid hammer noise.

The new clamps are normally raised to an intermediate stop position to=clear the railroad cars. This effects a reduction in thesize of the hydraulic power units as compared with existing systems where the clamps cannot be stopped in an intermediate position.

BRIEF STATEMENT OFTHE INVENTION In accordance with the present invention, there is provided a hydraulic clamping apparatus comprising in combination a first jaw member and a second jaw member in opposed clamping relation to eachother. The second jaw member is provided with an abutment. A hydraulically actuated extensible arm coacts between the first and second jaw members for moving them toward and away from each other. To anchor the extensible arm to the second jaw member, means are provided which include a floating mounting plate secured to the arm and constructed for seating engagement against the abutment in opposition to a load on the arm tending to separate the jaws and for movement away from the abutment when the load on the arm exceeds a predetermined value. Resilient means are provided for biasing the mounting plate against the abutment with a predetermined force which is determinative of the predetermined load. In specific embodiments of the invention, means are included for prestressing the resilient biasing means to exert the predetermined force. The extent of prestressing in a four-clamp installation is usually onefourth of the weight of the car and its cargo.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 shows a car dumper'railroad car clamp of the split type embodying the present invention and located in a rotary railroad car dumper partly shown in dotted lines and showing the clamp in a fully raised position,

an intermediate position, and in a clamping position against the marginal edge of the railroad car. The railroad car dumper is of the conventional tilting-track section type.

FIG. 2 is a top view of the clamp shown in FIG. 1 as it appears in the plane indicated by the line 22 of FIG. 1.

FIG. 3 is a side elevation of a clamping mechanism shown in FIG. 1 as it appears in the plane indicated by the line 3-3 in FIG. 1.

FIG. 4 is a detail on an enlarged scale of the anchoring means for the fixed extremity of the hydraulic actuating arm and showing a prestressed coil spring for biasing the lower end of the arm in abutting relation with the cradle of the car dumper.

FIG. 5 is a diagram showing a hydraulic lay-out for operating the extensible arm in the clamp mechanism of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS Referring now more particularly to FIGS. 1 3 inclusive, there is shown in FIG. 1 in dotted lines a representation of an end ring of a conventional rotary railroad car dumper cradle having disposed therein a platform 12 for supporting rails such as rail 14 upon which there is shown a gondola-type railway car 16. The railroad car 16 is carried on a bolster 18 which is in turn supported on coil springs such as spring 20. Secured in the cradle 10 adjacent the end ring is a clamping mechanism 22 embodying the principles of the present invention.

The clamping mechanism includes an upper jaw member 24. The second jaw member of the clamp may be regarded as the rail 14 carried by the platform 12 which is in turn secured to the cradle 10 in a known manner. The clamping force exerted between the upper jaw 24 and the rail 14 (second jaw) is provided by means of the hydraulically actuated extensible arm 26 which is movable into and out of hydraulic cylinder 28 in response to movement of hydraulic fluid from the pump 30.

The distal extremity 32 is attached by means of a pin 34 (shown in FIG. 2) to a clevis 36, which is in turn secured to a crosshead 38. Crosshead 38 joins together for unitary movement split jaw members 40 and 42 having car edge-engaging plates 44 and 46, respectively, attached thereto. Jaw members 40 and 42 are provided on their outer surfaces with guide channels 48 and 50, respectively, of U-shaped cross-section for guiding coaction with vertical bars 52 and 54 secured in a box-like framework generally indicated at 56. The framework 56 is in turn suitably fixed to the cradle 10 as by mounting plates 58 and 60. The ways 52 and 54 guide the channels 48 and 50 through the entire stroke of the extensible arm 26. To stabilize the jaws 40 and 42, a second guide channel such as guide channel 49 (FIG. 1) is provided in spaced relation to guide channel 48 on the jaw member 40. In like manner, a second guide channel is also provided on the jaw member 42 adjacent its lower extremity for guiding coaction with guide channel 50.

As shown in solid lines in FIG. 1, the jaw member 40 is at its extreme extension. It is split in order to clear end ring structure 11 as shown in FIG. 3. This position of the clamping mechanism is used in order that a locomotive may pass through the rotary car dumper cradle 10 without colliding with the jaw 24. The lowest position shown in dotted lines is below the marginal edge of the railroad car 16 in order that clamping action may occur within the total stroke of the extensible arm 26. The position betweeen maximum extension shown in solid lines and the minimum extension shown in the lower dotted lines is an intermediate position to which the clamp is normally raised when only railroad cars as distinct from a locomotive are passing through the car dumper. This means that in normal operation after the locomotive has passed through the cradle 10, the jaw will be extended only to the intermediate position as shown in FIG. 1. It will be observed that in this position, the hydraulic pump 30 will be delivering fluid under pressure to the hydraulic cylinder 28 at a maximum feed rate. Stopping in this position imposes excessive hydraulic shock upon the system in the absence of the structure hereinafter described.

Referring now more particularly to FIG. 4, which is a fragmentary cross-sectional view on an enlarged scale, the lower extremity of the hydraulic cylinder 28 is provided with a clevis 62. By means of a clevis pin 64, the clevis 62 is secured to a tongue 66 provided at its lower extremity with a floating mounting plate 68. The floating mounting plate 68 is normally in abutting relation with abutment 70 which is fixed as by welding to the framework of the cradle 10.

The floating mounting plate 68 has secured to the lower surface thereof as by welding an elongated pin 72 threaded at its distal extremity 74. Lockable nuts 76 and 78 in combination with washer 80 provide an adjustable support for a coil spring seat 82 which is slidably fitted over the end of pin 72 by means of an oversized bore 84 centrally thereof. The seat 82 is conveniently provided with a projecting portion 86 suitably sized for insertion within a heavy coil spring 88. The underside of the abutment plate 70 is also provided with a suitably sized collar 90 dimensioned for insertion within the coil spring 88. By the mechanism of the coil spring coacting between the bottom of the abutment plate 70 and the spring seat 82 and transmitting its bias through the washer 80 and the lockable nuts 76 and 78 to the pins 72 and in turn to the floating mounting plate 68, the system is able to withstand loads up to a predetermined load without movement of the floating plate 68 and loads in excess thereof within the prestressed biasing spring by compressing it further. Thus by axial adjustment of the position of the seat 82 with adjusting nut 78 being held in position by lock nut 76, any predetermined bias between the bottom of the abutment plate 70 and the floating mounting plate 68 may be secured.

When the load on the cylinder 28 exceeds the oppositely directed load imposed by the bias of spring 88, the floating mounting plate 68 will move away from the abutment plate 70. In order to limit the extent of travel of the mounting plate 68 away from the abutment plate 70, there are provided stop means of any suitable design. In the preferred embodiment shown in FIG. 4, the stop means include studs 92 and 94 suitably anchored to the abutment plate 70 as by means of heads 96 and 98 seated in suitable shouldered recesses 100 and 102, respectively, and welded into position as by weldment 104. Studs 92 and 94 extend through oversized bores 106 and 108 in floating plate 68, respectively. Flanged nuts 110 and 112 are threadedly secured to the distal extremities of the studs 92 and 94 and are adapted to seat against the floating plate 68 or washers such as washers 113 and 115 surrounding studs 92 and 94.

The present invention also includes in a single package a compact motor and pump assembly generally indicated at 114. The manner in which the apparatus is 5 constructed enables the provision of a modular clamping unit which by means of suitable brackets such as brackets 58 and 60 may be secured upon suitable mounting plates within a cradle such as cradle 10. The clamp hydraulic power unit 114 includes all of the elements necessary for delivering hydraulic fluid under pressure for opening and closing the clamp such as that shown in FIGS. 1 4 inclusive. Thus, preassembled and pretested modular units may be delivered to the field for installation in the car dumper. Ordinarily, four of such units are so utilized. Construction of the units in modular form greatly minimizes the cost of installation of clamps in the car dumper, saves plumbing, cuts down leakage, minimizes contamination, reduces filtration, reduces air ingestion, enables ready replacement of a malfunctioning unit, and also enables accurate setting of the units under controlled conditions rather than those which obtain in the field.

FIG. 5 shows a hydraulic circuit employing conventional symbols for operating the hydraulic clamps of the present invention. In accordance with the hydraulic diagram, there is provided and schematically shown a hydraulic fluid reservoir 116 having an immersion heater 118 therein. By means of suction line 120, variable displacement pump 122 driven by motor 124 through flexible coupling 126 delivers fluid to a fourway valve 128. This is a solenoid-operated valve. When solenoid A is operated, the spool 130 is moved into position to allow communication between the line 132 and the flow control valve assembly generallyindicated at 134. Fluid under pressure then flows through the swivel joint 136 through flexible hose portion 138 and swivel joint 140 into the cylinder 28 to drive extensible arm 26 in an upward direction.

Simultaneously with this, fluid flows out of the upper portion of cylinder 28 through swivel joint 142, flexible line 144, and swivel joint 146 through flow control unit 148 and by-passing check valve 150 through drain line 152 for return to the reservoir through return line 154. When solenoid B is activated, the flow of fluid through the spool is reversed, and pressurized fluid flows into the upper part of cylinder 28 through swivel joint 146, flexible hose 144, and swivel joint 142.

The solenoids in the hydraulic system and other controls are conveniently operated by limit switches such as that shown, for example, in FIG. 2 and identified by the numeral 156. This may be operated by a tripper 158 in a known manner. The positioning and operation of such limit switches is well known to those skilled in the art.

Accordingly, when hydraulic fluid under pressure flows through the upper end of the cylinder 28 and out the lower extremity of the cylinder 28, the clamp is moved into clamping position with the top of a railroad car such as shown in dotted lines fragrnentarily in FIG. 5. The shock of impact upon the marginal edge of the railroad car is taken within the coil spring 88. If the load exceeds the prestressed loading on the spring 88, the floating plate 68 may move away from the abutment plate 70 in the manner explained above and allow the spring 88 to absorb the load. Also, when the clamp is caused to stop at a position intermediate of the full stroke of the extensible arm 26, the hydraulic fluid hammer eflect is conveniently absorbed by the spring 88. The clamp may be stopped at an intermediate position by means of a limit switch and striker assembly, e.g., limit switch 156 and striker 158, operative to stop the pump 122 and a check valve, e.g. valve or 151, to hold the clamp at such position.

In order to make sure that there is pressure on the system during the dumping operation, there is provided a pressure-sensitive switch 147. If no pressure is registered on this switch, it automatically turns off and stops further action of the dumping. When the pressure is sufficient to hold the car, the switch is maintained closed and permits continuation of the dumping cycle.

There has thus been provided a clamping mechanism which is especially adapted for use in a rotary railroad car dumper. It is characterized by an hydraulically actuated extensible arm coacting between first and second jaw members, causing them to move toward and away from each other. Means are provided for anchoring the extensible arm to the second jaw member and include a floating mounting plate secured to the arm and constructed for seating engagement against an abutment which is in turn a part of the second jaw member. The engagement against the abutment is in opposition to a jaw-separating load on the arm and the ability of the mounted plate to float permits movement away from the abutment when the load on the arm exceeds a predetermined load. Spring means are provided for biasing the mounting plate against the abutment with a predetermined force which is determinative of the predetermined load. Meansare provided to stop the clamp in an intermediate position.

What is claimed is:

1. A hydraulic clamping apparatus comprising in combination:

a. a first jaw member;

b. a second jaw member in opposed clamping relationship to said first jaw member and having an abutment;

c. a hydraulically actuated extensible arm attached at one extremity to said first jaw member and anchored at its other extremity to said second jaw member for moving said jaw members toward and away from each other;

d. means for anchoring said extensible arm to said second jaw member, said means including:

1. a floating'mounting plate secured to said am at said other extremity and constructed for seating engagement against said abutment in opposition to a jaw separating load on said arm, and for movement away from said abutment when said load on said arm exceeds a predetermined load, and

2. resilient means for biasing said mounting plate against said abutment with a predetermined force determinative of said predetermined load.

2. An apparatus in accordance with claim 1 additionally including means for limiting the extent of movement of the mounting plate away from the abutment.

3. An apparatus in accordance with claim 1 additionally including means for prestressing said resilient biasing means to exert said predetermined force.

4. An apparatus in accordance with Claim 3 wherein said resilient biasing means is a coil spring and said prestressing means coacts between the abutment and the floating mounting plate and includes:

a. a pin axially of said coil spring; b. a stop mounted on said pin for receiving one end of said coil spring; and

c. adjustable means for locating said stop on said pin to apply a compressive stress to said spring.

5. An apparatus in accordance with claim 4 wherein the axial pin is attached to the mounting plate and extends through the abutment.

6. An apparatus in accordance with claim 4 also including means for limiting the extent of movement of the floating mounting plate away from the abutment.

7. An apparatus in accordance with claim 6 wherein the movement limiting means includes a stud anchored to the abutment and extending through the floating mounting plate, and a stop on said stud spaced from said mounting plate and dimensioned to intercept and prevent further movement of said mounting plate in a direction away from the abutment.

8. An apparatus in accordance with claim 1 also including means for stopping the movement of the arm at a position intermediate the full stroke thereof.

9. An apparatus in accordance with claim 8 wherein the arm stopping means includes a striker, a coacting limit switch, and a check valve coacting with said hydraulically actuated extensible arm to hold the latter in said intermediate position.

10. A rotary railroad car dumper for emptying the contents of a railroad car comprising in combination:

a. a rotatable cradle including a section of railroad trackway invertible therewith;

b. a hydraulic clamping apparatus attached at one end to the cradle for clamping the railroad car to the trackway during inversion and having:

0. a movable jaw member for clamping engagement with a railroad car;

(1. a hydraulically actuated extensible arm coacting between said movable jaw member and said cradle for moving the jaw member toward and away from said trackway;

e. means for anchoring said extensible arm to said cradle and including:

1. a floating mounting plate secured to said arm and constructed for seating engagement with said cradle in opposition to a load acting to extend said arm, and for movement away from said cradle when said load exceeds a predetermined value; and

2. resilient means for biasing said mounting plate against said cradle with a predetermined force determinative of said predetermined value.

1 1. A modular hydraulic clamping apparatus for a rotary railroad car dumper, said dumper including an abutment surface for said clamping apparatus, said clamping apparatus comprising in combination:

a. a movable jaw member;

b. a hydraulically actuated extensible arm for extending and retracting said movable jaw member;

c. means for anchoring the other end of said extensible arm to said abutment surface including:

1. a floating mounting plate secured to said arm and constructed for seating engagement against said abutment in opposition to a jaw separating load on said arm, and for movement away from said abutment when said load on said arm exceeds a predetermined load, and

2. resilient means for biasing said mounting plate against said abutment with a predetermined force determinative of said predetermined load; and

d. means for pumping hydraulic fluid to and from said extensible arm, said elements (a), (b), (c), and

(d) comprising a modular unit readily removable from and installable in said rotary railroad car dumper. 

1. A hydraulic clamping apparatus comprising in combination: a. a first jaw member; b. a second jaw member in opposed clamping relationship to said first jaw member and having an abutment; c. a hydraulically actuated extensible arm attached at one extremity to said first jaw member and anchored at its other extremity to said second jaw member for moving said jaw members toward and away from each other; d. means for anchoring said extensible arm to said second jaw member, said means including:
 1. a floating mounting plate secured to said arm at said other extremity and constructed for seating engagement against said abutment in opposition to a jaw separating load on said arm, and for movement away from said abutment when said load on said arm exceeds a predetermined load, and
 2. resilient means for biasing said mounting plate against said abutment with a predetermined force determinative of said predetermined load.
 2. An apparatus in accordance with claim 1 additionally including means for limiting the extent of movement of the mounting plate away from the abutment.
 2. resilient means for biasing said mounting plate against said abutment with a predetermined force determinative of said predetermined load.
 2. resilient means for biasing said mounting plate against said abutment with a predetermined force determinative of said predetermined load; and d. means for pumping hydraulic fluid to and from said extensible arm, said elements (a), (b), (c), and (d) comprising a modular unit readily removable from and installable in said rotary railroad car dumper.
 2. resilient means for biasing said mounting plate against said cradle with a predetermined force determinative of said predetermined value.
 3. An apparatus in accordance with claim 1 additionally including means for prestressing said resilient biasing means to exert said predetermined force.
 4. An apparatus in accordance with Claim 3 wherein said resilient biasing means is a coil spring and said prestressing means coacts between the abutment and the floating mounting plate and includes: a. a pin axially of said coil spring; b. a stop mounted on said pin for receiving one end of said coil spring; and c. adjustable means for locating said stop on said pin to apply a compressive stress to said spring.
 5. An apparatus in accordance with claim 4 wherein the axial pin is attached to the mounting plate and extends through the abutment.
 6. An apparatus in accordance with claim 4 also including means for limiting the extent of movement of the floating mounting plate away from the abutment.
 7. An apparatus in accordance with claim 6 wherein the movement limiting means includes a stud anchored to the abutment and extending through the floating mounting plate, and a stop on said stud spaced from said mounting plate and dimensioned to intercept and prevent further movement of said mounting plate in a direction away from the abutment.
 8. An apparatus in accordance with claim 1 also including means for stopping the movement of the arm at a position intermediate the full stroke thereof.
 9. An apparatus in accordance with claim 8 wherein the arm stopping means includes a striker, a coacting limit switch, and a check valve coacting with said hydraulically actuated extensible arm to hold the latter in said intermediate position.
 10. A rotary railroad car dumper for emptying the contents of a railroad car comprising in combination: a. a rotatable cradle including a section of railroad trackway invertible therewith; b. a hydraulic clamping apparatus attached at one end to the cradle for clamping the railroad car to the trackway during inversion and having: c. a movable jaw member for clamping engagement with a railroad car; d. a hydraulically actuated extensible arm coacting between said movable jaw member and saId cradle for moving the jaw member toward and away from said trackway; e. means for anchoring said extensible arm to said cradle and including:
 11. A modular hydraulic clamping apparatus for a rotary railroad car dumper, said dumper including an abutment surface for said clamping apparatus, said clamping apparatus comprising in combination: a. a movable jaw member; b. a hydraulically actuated extensible arm for extending and retracting said movable jaw member; c. means for anchoring the other end of said extensible arm to said abutment surface including: 